1. Field of the Invention
This invention relates generally to axisymmetric variable throat thrust vectoring nozzles and, more particularly, to such nozzles with bearing segments between an interface ring and a vectoring ring that is used to pivot nozzle flaps that vector the nozzle exhaust flow.
2. Discussion of the Background Art
An axisymmetric vectoring exhaust nozzle has been developed for military aircraft applications as disclosed in U.S. Pat. No. 4,994,660, issued to Hauer. The axisymmetric vectoring exhaust nozzle provides thrust vectoring for an axisymmetric convergent/divergent nozzle by universally pivoting the divergent flaps of the nozzle in an asymmetric fashion or, in other words, pivoting the divergent flaps in radial and tangential directions with respect to the unvectored nozzle centerline. This increases maneuverability of the aircraft, both for air to air combat missions and complicated ground attack missions.
Aircraft designers seek to replace or augment the use of conventional aerodynamic surfaces such as flaps and ailerons with vectorable nozzles which turn or vector the exhaust flow and thrust of the gas turbine engine powering the aircraft. The flaps are pivoted by a vectoring ring which can be axially translated and gimballed or tilted about its horizontal and vertical axis (essentially have its attitude adjusted) through a limited range. The vectoring ring is a generally hollow annular structure including radially spaced coaxial inner and outer walls and longitudinally spaced forward and aft walls. The vectoring ring may also be hollow and include internal struts forming a ring stiffening means as described in U.S. Pat. No. 5,820,024.
Vectored thrust produces tangential and radial loads referred to as side loads that are transmitted from the flaps by various load paths back to the engine casing through the actuators. These tremendous loads require heavy actuators to absorb the loads and, particularly, the bending moments exerted on the actuator shafts by thrust vectoring. U.S. Pat. No. 5,174,502, issued to Lippmeier et al., discloses a support for the vectoring ring that transfers at least a portion of the side loads acting generated by a gas turbine engine thrust vectoring nozzle to a relatively stationary portion of the engine. U.S. Pat. No. 5,174,502 discloses an apparatus to minimize or eliminate the side loads transferred by the nozzle to the actuators, reduce or eliminate the bending moments that the actuators would be subject to due to the radial loads, and to minimize the size and weight of the nozzle actuators and hydraulic system used to power the actuators. The support includes pivotal links that allow two degree of freedom (2 DOF) pivoting or gimballing motion and axial translation of the vectoring ring. One of the embodiments has a dual link support means with a rectangular first link pivotally attached to the engine casing by a hinge. The first link is pivotally connected to a second link which in turn is universally hinged to the vectoring ring by a 3 DOF or spherical joint.
Vectoring ring support and actuation apparatuses disposed in an equi-angular manner circumferentially about the engine casing are disclosed in U.S. Pat. No. 6,199,772. A support pivoting means and ring gimballing means allows the vectoring ring attitude adjustments by a set of linear actuators. The vectoring ring support apparatus transfers side loads acting on a vectoring ring and generated by a gas turbine engine thrust vectoring nozzle to a relatively stationary portion of the engine and allows tilting of the vectoring ring to vector the thrust of the nozzle. Each linear actuator is connected by a slider bar to the vectoring ring, a first actuator joint connects the linear actuator to a forward end of the slider bar, and an aft actuator joint connects an aft end of the slider bar to the vectoring ring.
Many modem fighter aircraft systems have an exhaust nozzle interface that provides an aerodynamically smooth transition from the aircraft fuselage to the aircraft engine exhaust nozzle. A typical nozzle interface includes an aircraft tail cone assembly, an exhaust nozzle, and a sealing mechanism between the two often called as xe2x80x9cturkey feathersxe2x80x9d or xe2x80x9ceagle feathersxe2x80x9d. The turkey feathers are often an integral part of the aircraft tail cone assembly and are often attached to the aircraft tail cone assembly with rivets. The aircraft tail cone assembly is usually attached to the aircraft fuselage with bolts or screws. The interface allows for relative motion between the aircraft and aircraft engine that may occur due to differential radial and axial thermal expansion and differential radial motion due to aircraft applied maneuver loads and/or gyroscopic moments. It is desirable that an interface provides good air sealing between the aircraft and aircraft engine for all aircraft and engine operating conditions, has a lightweight and low cost design which minimizes aerodynamic drag, is easy to assemble and disassemble, is easy to maintain, and does not add significant radar cross section to the aircraft system.
The axisymmetric vectoring exhaust nozzle""s outer shroud is attached to an exhaust duct of the engine by a multitude of individual brackets known as shroud supports instead of being attached directly to or fabricated as part of the exhaust duct. The shroud supports are used because the movement of the vectoring ring requires the elimination of the section of the exhaust duct cone that would otherwise support the shroud as done in non-vectoring engines. The outer flaps translate axially while the outer shroud remains stationary thereby creating a step between the two components and subsequent undesirable additional aerodynamic drag.
Briefly, in accordance with one aspect of the present invention, an aircraft gas turbine engine axisymmetric vectoring nozzle has an interface ring centered about a nozzle centerline, a vectoring ring disposed radially inwardly of and apart from the interface ring, and a bearing radially disposed between the vectoring ring and the interface ring. In a more particular embodiment of the invention, the bearing is a sliding bearing having a sliding interface between the vectoring ring and the interface ring and the sliding interface is spherical in shape. In the exemplary embodiment of the invention, the bearing is constructed of bearing segments which are sliding bearing segments including sliding interfaces between the vectoring ring and the interface ring and the sliding interfaces are spherical in shape.
Each of the bearing segments includes an outer sliding element attached to the interface ring, an inner sliding element attached to the vectoring ring, and spherically curved outer and inner sliding surfaces on the outer and inner sliding elements respectively wherein the spherically curved outer and inner sliding surfaces define the sliding interfaces between the vectoring ring and the interface ring. At least one of the bearing segments has an outer sliding element that is circumferentially disposed and trapped between circumferentially spaced apart rails disposed on a corresponding one of the inner sliding elements. In a yet more particular embodiment of the invention, a plurality of interface ring support guides are disposed radially inwardly of and in sliding support relationship with the interface ring and located axially forward of the vectoring ring.
One embodiment of the present invention is an aircraft gas turbine engine axisymmetric vectoring exhaust nozzle apparatus having the vectoring ring operably linked to a plurality of pivotal flaps by universal joints, circumferentially disposed about a nozzle centerline, and bounding an exhaust gas flowpath in the nozzle. Each of the universal joints has at least two rotational degrees of freedom. A linear actuation and vectoring ring support apparatus is operably connected to the vectoring ring for actuating and supporting the vectoring ring. The apparatus includes a linear actuator connected by a slider bar to the vectoring ring, a first actuator joint connecting the linear actuator to a forward end of the slider bar, and an aft actuator joint connecting an aft end of the slider bar to the vectoring ring. The apparatus further includes a vectoring ring support for slidably supporting the slider bar, restraining circumferential movement of the vectoring ring, and transferring side loads acting on the vectoring ring to a relatively stationary portion of the engine. The interface ring is centered about the nozzle centerline and disposed radially outwardly of and apart from the vectoring ring, and the bearing is radially disposed between the vectoring ring and the interface ring. A plurality of interface ring support guides are disposed radially inwardly of and in sliding support relationship with the interface ring and located axially forward of the vectoring ring. The interface ring support guides are attached to a casing of the engine by a support structure mounted on the casing.
The present invention provides an interface between the aircraft and aircraft engine for all aircraft and engine operating conditions. The invention provides good air sealing, is lightweight, and has a low cost design which minimizes aerodynamic drag. The invention is easy to assemble and disassemble, is easy to maintain, and does not add significant radar cross section to the aircraft system. The present invention eliminates a step between the outer flaps which translate axially and the outer shroud which remains stationary and eliminates subsequent undesirable additional aerodynamic drag.